Transparent Bridge Network After STA Is

The spanning-tree calculation occurs when the bridge is powered up and whenever a topology change is detected. The calculation requires communication between the spanning-tree bridges, which is accomplished through configuration messages (sometimes called bridge protocol data units, or BPDUs). Configuration messages contain information identifying the bridge that is presumed to be the root (root identifier) and the distance from the sending bridge to the root bridge (root path cost)....

Addressing

As with all network-layer protocols, the addressing scheme is integral to the process of routing IP datagrams through an internetwork. An IP address is 32 bits in length, divided into either two or three parts. The first part designates the network address the second part (if present) designates the subnet address and the final part designates the host address. Subnet addresses are present only if the network administrator has decided that the network should be divided into subnetworks. The...

Adjusting Buffers

Excessively high bandwidth utilization over 70 results in reduced overall performance and can cause intermittent failures. For example, DECnet file transmissions might be failing due to packets being dropped somewhere in the network. If the situation is bad enough, you must increase the bandwidth of the link. However, increasing the bandwidth might not be necessary or immediately practical. One way to resolve marginal serial line overutilization problems is to control how the router uses data...

Apple Talk Configuration and Troubleshooting Tips

This section offers configuration and troubleshooting tips that can help you prevent or more easily repair problems in AppleTalk internetworks. It consists of information on preventing AppleTalk problems, preventing internetwork reconfiguration problems, changing zone names, using AppleTalk Discovery Mode, and forcing an interface up to allow a router to start functioning if the network is misconfigured. Table 9-1 lists suggestions to help you avoid problems when configuring a router for...

Apple Talk Enhanced IGRP Clients Cannot Connect to Servers

Symptom Macintosh clients cannot connect to servers in an AppleTalk Enhanced IGRP network environment. Table 9-11 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-11 AppleTalk Enhanced IGRP Clients Cannot Connect to Servers Table 9-11 AppleTalk Enhanced IGRP Clients Cannot Connect to Servers For information on troubleshooting this problem, see the section AppleTalk Enhanced IGRP Routers Not Establishing Neighbors later in this chapter. For...

Apple Talk Enhanced IGRP Router Stuck in Active Mode

Symptom An AppleTalk Enhanced IGRP router is stuck in Active mode. The router repeatedly sends error messages similar to the following to the console DUAL-3-SIA Route 2.24 Stuck-in-Active Note Occasional messages of this type are not a cause for concern. This is how an Enhanced IGRP router recovers if it does not receive replies to its queries from all its neighbors. However, if these error messages occur frequently, you should investigate the problem. For a more detailed explanation of...

Apple Talk Enhanced IGRP Routes Missing from Routing Table

Symptom Routes are missing from the routing table of routers running AppleTalk Enhanced IGRP. Clients (Macintosh computers) on one network cannot access servers on a different network. Clients might or might not be able to connect to servers on the same network. The problem might occur in internetworks running only Enhanced IGRP or in an internetwork running Enhanced IGRP and RTMP. Table 9-13 outlines the problems that might cause this symptom and describes solutions to those problems.

Apple Talk Technology Basics

AppleTalk was designed as a client server distributed network system. In other words, users share network resources (such as files and printers) with other users. Computers supplying these network resources are called servers computers using a server's network resources are called clients. Interaction with servers is essentially transparent to the user because the computer itself determines the location of the requested material and accesses it without further information from the user. In...

Apple Talk Users Cannot Access Zones or Services

Symptom Users cannot access zones or services that appear in the Chooser. Users might or might not be able to access services on their own network. Table 9-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 9-2 AppleTalk Users Cannot Access Zones or Services Duplicate network numbers or overlapping cable-range Step 1 Use the show appletalk interface exec command. Check the output for a port configuration mismatch message. If the command output...

Arp

ARP entities are classified as either address resolution clients or address resolution services. Address resolution clients are usually implemented in client nodes, whereas address resolution services are typically provided by service nodes. An ARP packet has an 8-byte header consisting of a 2-byte packet type, a 4-byte network number, and a 2-byte subnetwork number. There are four packet types a query request, which is a request for an ARP service a service response, which is a response to a...

ATM Label Switching

ATM uses label switching, a technique in which a simple label is placed in the header of each cell. The label provides information used in transporting the cell across the next hop in the network. Networks that do not use label switching usually require each packet (or cell) to contain the explicit address of the final destination. ATM uses label switching because it is simpler, thereby making faster switching possible. 1 A switching unit reads an incoming cell from a particular port. The...

Audience

Internetworking Troubleshooting Handbook is intended for network administrators who are responsible for troubleshooting internetworks that implement Cisco products and Cisco-supported protocols. Administrators should have hands-on experience in configuring, administering, and troubleshooting a network, should know how to configure routers, switches and bridges, and should be familiar with the protocols and media that their hardware has been configured to support. Awareness of the basic topology...

Basic Port Checks

The following steps outline the procedure for performing basic port checks. It is important to perform basic port checks to verify that a LightStream 2020 port is enabled and functioning correctly Step 1 Use the show port port-number all command to display information about a port. Step 2 Check the Admin Status field to make sure that the port is up. Step 3 Check for excessive line errors, packet drops, or a lack of receive data. If there is no receive data or if the error rate on the receive...

Booting Client ARP Requests Timeout During Netboot

Verify that neighbor routers can ping the server. Use the trace exec command to determine the path to the server. Use the show arp privileged exec command to examine the ARP1 tables or the show ip route privileged exec command to view the IP routing table. Verify that the server is listed and that the routing table entries are appropriate. Use the clear arp-cache and clear ip-route privileged exec commands to force the router to repopulate its ARP and routing tables. Shut down all extra...

Booting Invalid Routes Prevent Netbooting

Symptom Invalid routes prevent successful netbooting. If the router is sending packets over an invalid path, a message similar to one of the following is displayed on the console Booting gs3-bfx OOOO timed out Booting gs3-bfx .O.O.O.O timed out In some cases, there might be an initial response from a server but the netboot sequence still fails. The boot message would be similar to the following Table 3-16 outlines the problems that might cause this symptom and describes solutions to those...

Booting Router Hangs After ROM Monitor Initializes

Symptom When a user is booting a Cisco 7000 series, AGS+, AGS, ASM-CS, MGS, IGS, or CGS router from ROM, the system hangs after the ROM monitor initializes. Table 3-19 outlines the problems that might cause this symptom and describes solutions to those problems. Table 3-19 Booting Router Hangs After ROM Monitor Initializes Table 3-19 Booting Router Hangs After ROM Monitor Initializes Inspect EPROM size jumpers. Refer to the hardware installation and maintenance publication for your router to...

Booting the Router

Cisco routers can initialize the system (boot) in four ways Netboot Routers can boot from a server using the Trivial File Transfer Protocol (TFTP), the DEC Maintenance Operation Protocol (MOP), or the Remote Copy Protocol (RCP) across any of the supported media types (such as Ethernet, Token Ring, Fiber Distributed Data Interface FDDI , High-Speed Serial Interface HSSI , and serial lines). Flash memory Routers can boot from Flash memory, a nonvolatile storage medium that can be electrically...

Booting Timeouts and Outof Order Packets Prevent Netbooting

Symptom Timeouts or out-of-order packets prevent successful netbooting. The number oftimeouts and out-of-order packets indicated on the router's console display might vary. The following example shows a netbooting session that contains excessive timeouts and out-of-order packets Booting gs3-bfx from 131.108.1.123 O.O .O O OOO.O .O.O The client router might boot in this situation. However, when excessive timeouts and out-of-order packets occur, there is probably a network problem, and netbooting...

Breakout Boxes Fox Boxes and BERTsBLERTs

Breakout boxes, fox boxes, and bit block error rate testers (BERTs BLERTs) are digital interface testing tools used to measure the digital signals present at PCs, printers, modems, the channel service unit digital service unit (CSU DSU), and other peripheral interfaces. These devices can monitor data line conditions, analyze and trap data, and diagnose problems common to data communication systems. Traffic from data terminal equipment (DTE) through data communications equipment (DCE) can be...

Catalyst 1600 Token Ring Switch Startup

When you start up a Catalyst 1600 Token Ring switch, the self-test program automatically checks to see whether the switch is operating correctly. The self-test begins by testing low-level hardware functions and then conducts high-level self-tests. During the high-level self-test, the LCD panel displays the following The version number of the boot software, and the date and time that the software was released The number of each stage in the self-test (these are usually displayed too quickly for...

Catalyst 2900 Series Startup

When you start up a Catalyst 2900 series LAN switch, the following should occur The PS LED on the supervisor engine module faceplate should come on and stay green while power is applied to the system. The system fan assembly and Fan LED should come on and stay on while power is applied to the system. The Status LED on the supervisor engine module and on each interface should be orange until the boot is complete. When the system boot is complete, the supervisor engine module initializes the...

Catalyst 3000 Series Startup

When you start up a Catalyst 3000 series LAN switch, the following should occur The Power LED should come on. The fan should begin operating and should stay on while power is applied to the system. On some models, the DIAG LED should come on, stay on for the duration of the system's self-test diagnostics, and then turn off. While booting, the console screen displays a script and system banner, which should be similar to the following Cisco Catalyst Boot Firmware P N 57-1327-02, Copyright 1995 -...

Catalyst 5000 Series Startup

When you start up a Catalyst 5000 series LAN switch, the following should occur The PS1 and PS2 LEDs on the supervisor engine module faceplate should be green. The system fan assembly should be operating and the Fan LED on the supervisor engine module should come on. The Status LED on the supervisor engine module and all interfaces should be orange until the boot is complete. When the system boot is complete, the supervisor engine module should initialize the switching modules. The status LED...

Cell Relay Packet Handling

Cell relay is a flexible and responsive method for multiplexing all forms of digital traffic (data, voice, image, and video). Cell relay can handle rapid changes in the quantity and pattern of the traffic in the network. All traffic is placed in fixed-length packets of information (cells) and switched at high speeds. Cell relay is generally acknowledged as the best multiplexing technology for modern communication applications because it combines the strengths of TDM and conventional packet...

Characteristics dcebitrate Kbits dtebitrate bits

Set the DCE or DTE bit rate for the specified port, depending on the dce-dte-type value described below. The value of Kbits for the DCE bit rate may be 56, 64, 128, 192, 256, 384, 448, 512, 768, 896, 1344, 1536, 1792, 2688, 3584, 4000, or 5376. The value of bits for the DTE bit rate is unrestricted in the range of decimal integers 9,000 6,000,000. Step 3 Compare the Measured Bit Rate with the Admin DCE Rcv Bit Rate field. If the value shown in the Measured Bit Rate field is significantly...

Cip Claw Connection Does Not Come Up

Symptom Common Link Access for Workstations (CLAW) connections do not come up properly over a Channel Interface Processor (CIP). The output of the show extended channel slot port statistics exec command shows N for CLAW connections, indicating that they are down. Table 10-13 outlines the problems that might cause this symptom and describes solutions to those problems. Table 10-13 CIP CLAW Connection Does Not Come Up Table 10-13 CIP CLAW Connection Does Not Come Up Step 1 Check whether TCP IP is...

Cisco 4000 and Cisco 3000 Series Startup

When you start up a Cisco 4000 or a Cisco 3000 series router, the following should occur The System OK LED should come on and stay on as long as power is supplied. The fans should be operating. When the system has initialized successfully, the system banner should be displayed on the console screen. The system banner should look similar to the following System Bootstrap, Version 4.14(9), SOFTWARE Copyright (c) 1986-1994 by cisco Systems 4000 processor with 16384 Kbytes of main memory Loading...

Cisco 7000 Series Startup

When you start up a Cisco 7000 series router, the following should occur The DC OK LED should go on and should remain on as long as the system is receiving source power. The fans should be operating. The Route Processor (RP) Normal LED should go on and stay on to indicate normal system operation the Halt CPU LED should remain off. The Enabled LED on the Switch Processor (SP) or Silicon Switch Processor (SSP) and each interface processor should go on when the RP has completed initialization of...

Cisco 7500 Series Startup

When you start up a Cisco 7500 series router, the following should occur The AC (or DC) OK LED should go on immediately and should remain on as long as the system is receiving power. The blower should be operating. The Route Switch Processor (RSP) and front-panel Normal LEDs should go on (to indicate normal system operation) and should remain on during system operation the CPU Halt LED should remain off. The Enabled LED on each interface processor should go on (to indicate that the RSP has...

Cisco View Timeout Error Messages

Symptom When attempting to use the CiscoView application, you receive timeout messages and cannot view a device. Table 23-7 outlines the problems that might cause this symptom and describes solutions to those problems. Table 23-7 CiscoView Timeout Error Messages Table 23-7 CiscoView Timeout Error Messages Perform the steps outlined in the section Testing Basic Connectivity and Setup earlier in this chapter. Try increasing the polling interval. To increase the polling interval, select Options,...

Cisco Works Internetwork Management Software

CiscoWorks is a series of SNMP-based internetwork management software applications. CiscoWorks applications are integrated on several popular network management platforms and build on industry-standard platforms to provide applications for monitoring device status, maintaining configurations, and troubleshooting problems. Following are some of the applications included in the CiscoWorks product that are useful for troubleshooting your internetwork Device Monitor Allows the network manager to...

Cisco Works Sync with Sybase Fails

Symptom Attempts to run Sync with Sybase in CiscoWorks fail. Table 23-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 23-2 CiscoWorks Sync with Sybase Fails Table 23-2 CiscoWorks Sync with Sybase Fails Follow the steps outlined in the section Testing Basic Connectivity and Setup earlier in this chapter. Run nmadd from the command line to determine whether the problem is related to community string, name resolution, or timing out. The nmadd...

Clocking Overview

The CSU DSU derives the data clock from the data that passes through it. In order to recover the clock, the CSU DSU hardware must receive at least one 1-bit value for every 8 bits of data that pass through it this is known as ones density. Maintaining ones density allows the hardware to recover the data clock reliably. Newer T1 implementations commonly use Extended Superframe Format (ESF) framing with binary eight-zero substitution (B8ZS) coding. B8ZS provides a scheme by which a special code...

Configuration Management Deviceto Database or Databaseto Device Does Not

Symptom The device-to-database or the database-to-device operation in the Configuration Management application does not work. Table 23-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 23-5 Configuration Management Device-to-Database or Database-to-Device Does Not Run Table 23-5 Configuration Management Device-to-Database or Database-to-Device Does Not Run Perform the steps outlined in the section Testing Basic Connectivity and Setup Perform...

Configuration Register DIP Switch

Cisco 7000 series running Software Release 9.17(4) or later (Flash netboot) or Cisco IOS Release 10.0 or later (ROM) Cisco 7000 series running Software Release 9.17(4) or later (Flash netboot) or Cisco IOS Release 10.0 or later (ROM) Cisco 7000 running Software Release 9.21 or earlier from ROM Cisco IGS running Software Release 9.1 or later Cisco IGS running software prior to Software Release 9.1

Configuration SnapIn Manager Cannot Modify DoItNow

Symptom The DoItNow operation in the Configuration Snap-In Manager application does not work. Table 23-6 outlines the problems that might cause this symptom and describes solutions to those problems. Table 23-6 Configuration Snap-In Manager Cannot Modify DoItNow Table 23-6 Configuration Snap-In Manager Cannot Modify DoItNow Perform the steps outlined in the section Setup earlier in this chapter. Testing Basic Connectivity and Perform the steps outlined in the section earlier in this chapter....

Creating a Core Dump

To obtain a core dump when a router crashes, use the exception dump ip-address router configuration command (where ip-address is the address of your TFTP server). Including this command in your configuration causes the router to attempt to make a core dump when it crashes. The core dump is written to a file named hostname-core on your TFTP server, where hostname is the name of the router. You can change the name of the core file by configuring the exception core-file filename command. This...

Creating Core Dumps

When a router crashes, it is sometimes useful to obtain a full copy of the memory image (called a core dump> ) to identify the cause of the crash. Core dumps are generally useful only to your technical support representative. Note Use the commands discussed in this appendix only under the direction of a technical support representative. Creating a core dump while the router is functioning in a network can disrupt network operation. The resulting binary file, which is very large, must be...

Data Command Frames

Data command frames vary in size, depending on the size ofthe information field. Data frames carry information for upper-layer protocols command frames contain control information and have no data for upper-layer protocols. In data command frames, a frame control byte follows the access control byte. The frame control byte indicates whether the frame contains data or control information. In control frames, this byte specifies the type of control information. Following the frame control byte are...

Datagram Delivery Protocol

AppleTalk's primary network-layer protocol is the Datagram Delivery Protocol (DDP). DDP provides connectionless service between network sockets. Sockets can be assigned either statically or dynamically. AppleTalk addresses, which are administered by the DDP, consist of two components a 16-bit network number and an 8-bit node number. The two components are usually written as decimal numbers, separated by a period (for example, 10.1 means network 10, node 1). When an 8-bit socket identifying a...

DECnet Connections to DEC Hosts Fail over Router End Node Problem

Symptom DECnet nodes cannot communicate when attempting to make connections over routers. Note This section focuses on problems in end nodes. For router-related problems and solutions, see the section DECnet Connections to DEC Hosts Fail over Router (Router Problem) later in this chapter. Table 11-1 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-1 DECnet Connections to DEC Hosts Fail over Router (End Node Problem) Step 1 Check the end...

DECnet Connections to DEC Hosts Fail over Router Router Problem

Symptom DECnet nodes cannot communicate when attempting to make connections over routers. Note This section focuses on problems in the router. For end node-related problems and solutions, see the section DECnet Connections to DEC Hosts Fail over Router (End Node Problem) earlier in this chapter. Table 11-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-2 DECnet Connections to DEC Hosts Fail over Router (Router Problem) Use the show decnet...

DECnet End Nodes Cannot Find Designated Router

Symptom End nodes cannot find a designated router. End nodes cannot access nodes that are on different LANs, but other nodes connected to the same LAN are accessible. Table 11-3 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-3 DECnet End Nodes Cannot Find Designated Router DECnet not enabled on Step 1 Use the show running-config privileged exec command to view the router router configuration. Determine whether DECnet global configuration...

DECnet No Phase IV Connectivity over Phase V Backbone

Symptom Communication between DECnet Phase IV areas separated by an ISO CLNS (Phase V) backbone fails. Phase IV nodes cannot communicate with other Phase IV nodes across a Phase V cloud. However, nodes can communicate with one another within the same Phase IV cloud. Note For more information about troubleshooting DECnet OSI internetworks, see Chapter 12, Troubleshooting ISO CLNS. Table 11-7 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-7...

DECnet Poor Performance

Symptom Performance in a DECnet network is slow or unreliable. Connections to hosts over one or more routers are periodically inaccessible or drop unexpectedly. Table 11-9 outlines the problems that might cause this symptom and describes solutions to those problems. Step 1 Use the show decnet traffic exec command and check the Received and Forwarded fields in the output. In most cases, the values in these fields should match. Step 2 If the values do not match, check the Returned, Converted,...

DECnet Router or End Node Sees Incorrect Designated Router

Symptom Routers and end nodes see an incorrect or an unexpected designated router. If your network requires a specific router to be elected the designated router, allowing another router to become a designated router can cause unpredictable network behavior and can block connectivity in and out of the area. Table 11-4 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-4 DECnet Router or End Node Sees Incorrect Designated Router Priority of...

DECnet Routers Not Establishing Adjacencies

Symptom Routers do not establish adjacencies with other routers on the same LAN. Table 11-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 11-5 DECnet Router Not Establishing Adjacencies Router area number is higher than configured decnet max-area DECnet limits the number of adjacencies that can be established by a router to 32. Step 1 Enable the debug decnet events privileged exec command to determine whether the adjacency is being...

DECnet Routing Node Adjacencies Toggle Up and Down

Symptom Routing adjacencies toggle up and down. Output such as the following appears repeatedly on the DEC system console OPCOM 30-JUN-1993 1 25 07.45 DECnet event 4.16, adjacency rejected From NODE 12.1 (The Bay), 30-JUN-1993 1 25 07.45 Circuit UNA-0, Adjacent node 1.101 (Vax1) OPCOM 30-JUN-1993 1 25 07.46 Message from user DECNET on The Bay DECnet event 4.15, adjacency up From NODE 12.1 (The Bay), 30-JUN-1993 1 25 07.46 Circuit UNA-0, Adjacent node 1.12 (Vax2) This output indicates that...

Default Variable Values

The following sections provide the default values assigned to the CiscoWorks environment variables for each platform. On SunOS and HP-UX installations, the values assigned to the CiscoWorks environment variables should be similar to the following, provided that you chose the defaults during installation of the software PATH NMSROOT bin, NMSROOT etc, SYBASE bin If you did not load your software in the default directories, your values should point to the locations you chose. Use the printenv UNIX...

Descriptions of Environment Variables

The following are descriptions of the CiscoWorks environment variables NMSROOT Default directory for CiscoWorks installation. If the software was installed in a different directory, substitute the appropriate directory path to ensure the correct definition of the NMSROOT environment variable. SYBASE Default directory for Sybase installation. If the software was installed in a different directory, substitute the appropriate directory path to ensure the correct definition of the SYBASE...

Detecting Clocking Problems

To detect clocking conflicts on a serial interface, look for input errors as follows Step 1 Use the show interfaces serial exec command on the routers at both ends of the link. Step 2 Examine the command output for CRC, framing errors, and aborts. Step 3 If either of these steps indicates errors exceeding an approximate range of 0.5 to 2.0 of traffic on the interface, clocking problems are likely to exist somewhere in the WAN. Step 4 Isolate the source of the clocking conflicts as outlined in...

Dialin Modem Cannot Send or Receive IP Data

Symptom After a dialin connection is established, a modem cannot send or receive IP data. Note For general problems associated with a modem that cannot send or receive data, refer to the section Dialin Modem Cannot Send or Receive Data earlier in this chapter. Note For information on troubleshooting IP problems not specific to dialin connections, refer to Chapter 7, Troubleshooting TCP IP. Table 16-10 outlines the problems that might cause this symptom and describes solutions to those problems....

Dialin Modem Cannot Send or Receive IPX Data

Symptom After a dialin connection is established, a modem cannot send or receive Novell IPX data. Note For general problems associated with a modem that cannot send or receive data, refer to the section Dialin Modem Cannot Send or Receive Data earlier in this chapter. Note For information on troubleshooting Novell IPX problems not specific to dialin connections, refer to Chapter 8, Troubleshooting Novell IPX. Table 16-11 outlines the problems that might cause this symptom and describes...

Dialin Modem Hangs Up Shortly After Connecting

Symptom A dialin connection is successful but the modem hangs up after 30 to 90 seconds. Table 16-5 outlines the problems that might cause this symptom and describes solutions to those problems. Table 16-5 Dialin Modem Hangs Up Shortly After Connecting Possible Causes Suggested Actions Table 16-5 Dialin Modem Hangs Up Shortly After Connecting Use the show line exec command on the access server or router. The output for the auxiliary port should indicate the currently configured Tx1 and Rx2 For...

Dialin No Connectivity Between Modem and Router

Symptom The connection between a modem and a Cisco access server or router does not work. Attempts to initiate a reverse Telnet session to the modem have no result, or the user receives a connection refused by foreign host message. Note More specific symptoms for dialin connection problems are covered later in this chapter. Table 16-2 outlines the problems that might cause this symptom and describes solutions to those problems. Table 16-2 Dialin No Connectivity Between Modem and Router Possible...

Digital Network Architecture

Contrary to popular belief, DECnet is not a network architecture at all but is, rather, a series of products conforming to Digital's Digital Network Architecture (DNA). Like most comprehensive network architectures from large systems vendors, DNA supports a large set of both proprietary and standard protocols. The list of DNA-supported technologies grows constantly as Digital implements new protocols. Figure 11-1 illustrates an incomplete snapshot of DNA and the relationship of some of its...

Distance Vector Multicast Routing Protocol

Distance Vector Multicast Routing Protocol (DVMRP), defined in RFC 1075, uses a technique called reverse path flooding. With reverse path flooding, on receipt of a packet, the router floods the packet out all paths except the path that leads back to the source of the packet, which ensures that a data stream reaches all LANs. If the router is attached to a LAN that does not want to receive a particular multicast group, the router sends a prune message back to the source to stop the data stream....

Document Conventions

Our software and hardware documentation uses the following conventions The symbol A represents the key labeled Control. For example, AD means hold down the Control key while you press the D key. A string is defined as a nonquoted set of characters. For example, when setting up a community string for SNMP to public, do not use quotes around the string, or the string will include the quotation marks. Command descriptions use these conventions Examples that contain system prompts denote...

Document Organization

The Internetworking Troubleshooting Handbook provides the information necessary to troubleshoot many problems commonly encountered in internetworks using Cisco hardware and software products. This publication consists of the following six parts The chapters in Part 1, Introduction to Troubleshooting, provide an introduction to troubleshooting techniques and an overview of common troubleshooting tools. The chapters in Part 2, Hardware, Booting, and Media Problems, provide information for...

Environment Variable Locations

The location of environment variable definitions differs depending on the UNIX shell you are using. This will typically be the Korn shell (ksh), the C shell (csh), or the Bourne shell (sh). The default UNIX shell for a user ID is set up in the etc passwdfile. Use the set command to find out which shell you are using. The following section provides information on files that are reviewed by the C shell and the Korn shell during login C shell At login, the system reads the .cshrcfile in the user's...

Establishing a Reverse Telnet Session to a Modem

If you are running Cisco IOS Release 11.0 or earlier, you must establish a reverse Telnet session to configure a modem to communicate with a Cisco device. As long as you lock the data terminal equipment (DTE)-side speed of the modem (see Table 16-5 for information on locking the modem speed), the modem will always communicate with the access server or router at the desired speed. Be certain that the speed of the Cisco device is configured prior to issuing commands to the modem via a reverse...

Ethernet and IEEE 8023

Ethernet and IEEE 802.3 specify similar technologies. Both are CSMA CD LANs. Stations on a CSMA CD LAN can access the network at any time. Before sending data, CSMA CD stations listen to the network to see if it is already in use. If it is, the station wishing to transmit waits. If the network is not in use, the station transmits. A collision occurs when two stations listen for network traffic, hear none, and transmit simultaneously. In this case, both transmissions are damaged, and the...

Failure Types

When a system crashes, the ROM monitor reports a failure type. The failure type is important both in its own right and as a guide to interpreting the other information the system provides. Failure types are usually one of the following The system encounters a bus error when the processor tries to use a device or a memory location that either does not exist or does not respond properly. Bus errors typically indicate either a software bug or a hardware problem. The address the processor was...

Fault Management Mechanisms

Token Ring networks employ several mechanisms for detecting and compensating for network faults. For example, one station in the Token Ring network is selected to be the active monitor. This station, which can potentially be any station on the network, acts as a centralized source of timing information for other ring stations and performs a variety of ring maintenance functions. One of these functions is the removal of continuously circulating frames from the ring. When a sending device fails,...

Fault Tolerant Boot Strategies

Although netbooting is useful, network or server failures can make netbooting impossible. After you have installed and configured the router's Flash memory, configure the boot sequence for the router to reduce the impact of a server or network failure. The following order is recommended 1 Boot an image from Flash memory. 2 Boot an image using a netboot. Following is an example of how to configure a router with a fault-tolerant boot sequence. Enter configuration commands, one per line. End with...

Fault Tolerant Features

FDDI provides a number of fault-tolerant features, the most important of which is the dual ring. If a station on the dual ring fails or is powered down or if the cable is damaged, the dual ring is automatically wrapped (doubled back onto itself) into a single ring, as shown in Figure 5-4. In this figure, when Station 3 fails, the dual ring is automatically wrapped in Stations 2 and 4, forming a single ring. Although Station 3 is no longer on the ring, network operation continues for the...

FDDI Specifications

FDDI is defined by four separate specifications (see Figure 5-1) Media Access Control (MAC) Defines how the medium is accessed, including frame format, token handling, addressing, an algorithm for calculating a cyclic redundancy check value, and error recovery mechanisms. Physical Layer Protocol (PHY) Defines data encoding decoding procedures, clocking requirements, framing, and other functions. Physical Layer Medium (PMD) Defines the characteristics of the transmission medium, including the...

FDDI Technology Basics

FDDI specifies a 100-Mbps, token-passing, dual-ring LAN using a fiber-optic transmission medium. It defines the physical layer and media-access portion of the link layer, and is roughly analogous to IEEE 802.3 and IEEE 802.5 in its relationship to the Open System Interconnection (OSI) reference model. Although it operates at faster speeds, FDDI is similar in many ways to Token Ring. The two types of networks share many features, including topology (ring), media-access technique (token passing),...

FDDITalk No Zone Associated with Routes

Symptom Routers on an FDDI ring have routes to networks across the ring, but no zones are associated with the routes. The output of the show appletalk route command indicates no zone set for those routes. Note On other media, routes with no zone set are the result of other problems, such as ZIP storms. See the sections AppleTalk Zones Missing from Chooser and AppleTalk Network Services Intermittently Unavailable in this chapter for more information. Table 9-17 outlines the problem that might...

Figure 111 DNA and the OSI Reference Model

As Figure 11-1 shows, DNA supports a variety of media and link implementations. Among these are well-known standards such as Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), IEEE 802.2, and X.25. DNA also offers a traditional point-to-point link-layer protocol called Digital Data Communications Message Protocol (DDCMP) and a 70-Mbps bus used in the VAX cluster called the computer-room interconnect bus (CI bus).

Figure 112 A Dna Phase IV Routing Layer Header

The first field in a DNA Phase IV routing header is the routing flags field, which includes A return-to-sender bit that, if set, indicates that the packet is returning to the source. A return-to-sender-request bit that, if set, indicates that request packets should be returned to the source if they cannot be delivered to the destination. An intraLAN bit, which is on by default. If the router detects that the two communicating end systems are not on the same subnetwork, it turns the bit off....

Figure 114 Examples of DECnet Addresses

DECnet hosts do not use manufacturer-assigned Media Access Control (MAC)-layer addresses. Instead, network-level addresses are embedded in the MAC-layer address according to an algorithm that multiplies the area number by 1,024 and adds the node number to the product. The resulting 16-bit decimal address is converted to a hexadecimal number and appended to the address AA00.0400 in byte-swapped order, with the least significant byte first. For example, DECnet address 12.75 becomes 12363 (base...

Figure 152 show controllers cbus Command Output

Switch Processor 5, hardware version 11.1, microcode version 10.7 512 Kbytes of main memory, 128 Kbytes cache memory 4 256 byte buffers, 4 1024 byte buffers, 312 1520 byte buffers 1024 byte system buffer Restarts 0 line down, 0 hung output, 0 controller error FSIP 0, hardware version 1.0, microcode version 175.0 Microcode loaded from system Interface and attached cable information Interface 0 - Serial 0 0, electrical interface is Universal (cable unattached) 22 buffer RX queue threshold, 23...

Figure 154 show controllers mci Command Output

Electrical interface identified as type UNKNOWN, suggesting a hardware failure or improperly connected cable. MCI 1, controller type 1.1, microcode version 1.8 128 Kbytes of main memory, 4 Kbytes cache memory 16 system TX buffers, largest buffer size 1520 Restarts 0 line down, 0 hung output, 0 controllererror Interface 0 is Ethernet1, station address 0000.0c0-3b09 22 total RX buffers, 9 buffer TX queue limit, bufer size 1520 Transmitter delay is 0 microseconds Interface 1 is Serial2, electrical...

Figure 155 Extended ping Specification Menu

Datagram size 100 64 specification Extended commands n yes - Extended commands Source address selected option Data pattern OxABCD Oxffff - Data pattern Loose, Strict, Record, Timestamp, Verbose none specification Sweep range of sizes n Type escape sequence to abort. Sending 20, 64-byte ICMP Echos to 12 9.44.12.7, timeout is 2 seconds Packet has data pattern 0xFFFF Success rate is 100 percent, round-trip min avg max 1 3 4 ms In general, perform serial line ping tests as follows Step 1 Put the...

Figure 156 All Zeros 1500Byte ping Test

Target IP address 192.169.51.22 Repeat count 5 100 Datagram size 100 1500 Timeout in seconds 2 Extended commands n y Source address 192.169.51.14 Type of service 0 Set DF bit in IP header no Validate reply data no I Data pattern OxABCD 0x0000 Loose, Strict, Record, Timestamp, Verbose none Sweep range of sizes n Type escape sequence to abort. Sending 100, 1500-byte ICMP Echos to 192.169.51.22, timeout is 2 seconds Packet has data pattern 0x0000 Success rate is 100 percent (100 100), round-trip...

Figure 157 All Ones 1500Byte ping Test

Target IP address 192.169.51.22 Repeat count 5 100 Datagram size 100 1500 Timeout in seconds 2 Extended commands n y Source address 192.169.51.14 Type of service 0 Set DF bit in IP header no Validate reply data no Loose, Strict, Record, Timestamp, Verbose none Sweep range of sizes n Type escape sequence to abort. Sending 100, 1500-byte ICMP Echos to 192.169.51.22, timeout is 2 seconds Packet has data pattern 0xFFFF Success rate is 100 percent (100 100), round-trip min avg max 4 6 8 ms zounds

Figure 158 show buffers Command Output

Cookie-Monster> show buffers Buffer elements 401 in free list (500 max allowed) 87777499 hits, 0 misses, 0 created Small buffers, 104 bytes (total 120, permanent 120) 114 in free list (20 min, 250 max allowed) 70005538 hits, 6 misses, 2 trims, 2 created Middle buffers, 600 bytes (total 90, permanent 90) 88 in free list (10 min, 200 max allowed) 25696696 hits, 27 misses, 27 trims, 27 created Big buffers, 1524 bytes (total 90, permanent 90) total identifies the total number of buffers in the...

Figure 162 show line Command Output

Line 1, Location , Type Length 24 lines, Width 80 columns rate (TX RX) is 38400 38400, no parity, 2 stopbits, 8 databits abilities I Hardware Flowcontrol In, Hardware Flowcontrol Out Modem-Callout, Modem RI is CD Modem state I Line 1, Location , Type Length 24 lines, Width 80 columns rate (TX RX) is 38400 38400, no parity, 2 stopbits, 8 databits abilities I Hardware Flowcontrol In, Hardware Flowcontrol Out Modem-Callout, Modem RI is CD Modem state I Lial Chars Escape Hold Stop Start x none - -...

Figure 172 ISDN Physical Layer Frame Formats

A Activation bit B1 B1 channel bits B2 B2 channel bits D D channel (4 bits x 4000 frames sec 16 kbps) E Echo of previous D bit F Framing bit L Load balancing S Spare bit The frames are 48 bits long, of which 36 bits represent data. The bits of an ISDN physical layer frame are used as follows F Provides synchronization. L Adjusts the average bit value. E Used for contention resolution when several terminals on a passive bus contend for a channel. B1, B2, and D For user data. Multiple ISDN user...

Figure 173 LAPD Frame Format

SAPI Service access point identifier (6 bits) C R Command response bit EA Extended addressing bits TEI Terminal endpoint identifier The LAPD Flag and Control fields are identical to those of HDLC. The LAPD Address field can be either 1 or 2 bytes long. If the extended address bit of the first byte is set, the address is 1 byte if it is not set, the address is 2 bytes. The first address field byte contains the service access point identifier (SAPI), which identifies the portal at which LAPD...

Figure 181 The Frame Relay Frame

Field length, 12 Variable 2 1 Field length, 12 Variable 2 1 The 10-bit DLCI value is the heart of the Frame Relay header. It identifies the logical connection that is multiplexed into the physical channel. In the basic (not extended by the LMI) mode of addressing, DLCIs have local significance that is, the end devices at two different ends of a connection may use a different DLCI to refer to that same connection. Figure 18-2 provides an example of the use of DLCIs in nonextended Frame Relay...

Figure 183

In LMI messages, the basic protocol header is the same as in normal data frames. The actual LMI message begins with 4 mandatory bytes, followed by a variable number of information elements (IEs). The format and encoding of LMI messages is based on the ANSI T1S1 standard. The first of the mandatory bytes (unnumbered information indicator) has the same format as the Link Access Procedure, Balanced (LAPB) unnumbered information (UI) frame indicator with the poll final bit set to 0. (For more...

Figure 192 X25 and the OSI Reference Model

End-to-end communication between DTEs is accomplished through a bidirectional association called a virtual circuit. Virtual circuits permit communication between distinct network elements through any number of intermediate nodes without the dedication of portions of the physical medium that characterizes physical circuits. Virtual circuits can be either permanent or switched (temporary). Permanent virtual circuits (PVCs) are typically used for the most often used data transfers, whereas...

Figure 194 The X121 Address Format

The addressing fields that make up the X.121 address are necessary only when an SVC is used, and then only during call setup. After the call is established, the PSN uses the LCI field of the data packet header to specify the particular virtual circuit to the remote DTE. Layer 3 X.25 uses three virtual circuit operational procedures call setup, data transfer, and call clearing. Execution of these procedures depends on the virtual circuit type being used. For a PVC, Layer 3 X.25 is always in data...

Figure 195

Bit stuffing is used to ensure that the flag pattern does not occur within the body of the frame. Address Indicates whether the frame carries a command or a response. Control Provides further qualifications of command and response frames, and also indicates the frame format (I, S, or U), frame function (for example, receiver ready or disconnect), and the send receive sequence number. 1 1 1 Variable 2 1 1 1 1 Variable 2 1 Data Carries upper-layer data. Its size and...

Figure 196 Output from the X25 Version of the show interfaces serial Command

SerialO is up, line protocol is up Hardware is MCI Serial Internet address is 131.63.125.14 255.255.255.0- MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec ely 255 255, load 1 255 Encapsulation X25, loopback not set __ I LAPB DTE, state CONNECT, modulo 8, k 7, N1 12056, N2 20 IFRAMEs 1 1 IRNRs 0 0 ReJs 0 0 SABM Es 1 0 FRMRs 0 Q DISCs 0 0 Not ready flow control count ress 170093, state R1 modulo 8, timer 0 Defaults cisco encapsulation, idle 0, nvc 1 input output window sizes 2 2, packet sizes 128...

Figure 201 A Transparent Bridging Table

The bridge uses its table as the basis for traffic forwarding. When a frame is received on one of the bridge's interfaces, the bridge looks up the frame's destination address in its internal table. If the table contains an association between the destination address and any of the bridge's ports aside from the one on which the frame was received, the frame is forwarded out the indicated port. If no association is found, the frame is flooded to all ports except the inbound port. Broadcasts and...

Figure 202 Inaccurate Forwarding and Learning in Transparent Bridging Environments

Suppose Host A sends a frame to Host B. Both bridges receive the frame and correctly conclude that Host A is on Network 2. Unfortunately, after Host B receives two copies of Host A's frame, both bridges again receive the frame on their Network 1 interfaces because all hosts receive all messages on broadcast LANs. In some cases, the bridges will then change their internal tables to indicate that Host A is on Network 1. If this is the case, when Host B replies to Host A's frame, both bridges...

Figure 203 A Transparent Bridge Network Before STA Is

The first activity in spanning-tree computation is the selection of the root bridge, which is the bridge with the lowest-value bridge identifier. In Figure 20-3, the root bridge is Bridge 1. Next, the root port on all other bridges is determined. A bridge's root port is the port through which the root bridge can be reached with the least aggregate path cost. The value of the least aggregate path cost to the root is called the root path cost. Finally, designated bridges and their designated...

Figure 205 The Transparent Bridge Configuration Message Format

The fields of the transparent bridge configuration message are as follows Protocol identifier Contains the value 0. Version Contains the value 0. Message type Contains the value 0. Flag A one-byte field, of which only the first 2 bits are used. The topology change (TC) bit signals a topology change. The topology change acknowledgment (TCA) bit is set to acknowledge receipt of a configuration message with the TC bit set. Root ID Identifies the root bridge by listing its 2-byte priority followed...

Figure 211 User Assignments on Communications Channel Using TDM

Time Time Time Time Time Time Time Time Time Time Time Time slot slot slot slot slot slot slot slot slot slot slot slot The time slots allocated for each user occur at precisely the same time in every frame. Because the time slots are synchronous, TDM is sometimes referred to as synchronous transfer mode (STM). Users can access the communications channel only when a time slot that has been allocated to them is available. For example, User A can send messages over the communications channel only...

Figure 2110 ATM Adaptation Layer Functions

When ATM cells are transferred through a network, each cell is processed in isolation from all other cells. All processing decisions are made based on the cell header no processing of the data in the payload field occurs. Figure 21-11 shows some examples of AAL processing. Figure 21-11 AAL Processing Examples Figure 21-11 AAL Processing Examples Hosts A and C are connected to the network through ATM interfaces, so they do all their AAL processing internally. The network does not do any...

Figure 2112 Information Flow Through AAL

Convergence sublayer (CS) user data is broken up into packets (CS-PDUs) Segmentation and reassembly (SAR) sublayer each CS-PDU is broken up into SAR-PDUs CS-PDU SAR-PDU SAR-PDU To ATM layer CS-PDU SAR-PDU SAR-PDU To ATM layer The convergence sublayer (CS) accepts higher-layer traffic for transmission across the network. Depending on the AAL type, header and or trailer fields are added to the packet. The packet is then segmented by the SAR sublayer to form 48-byte payloads (also known...

Figure 217 VCCs Transported Within VPs

Physical link in public or private network The ATM cell is the fixed-length transmission unit defined by the ATM standard. An ATM cell contains two major types of information the payload and the header. The payload is the information to be transferred through an ATM network. It can include data, voice, image, or video. The header is the information used to route the cell through the network and to ensure that the cell is forwarded to its destination. Every ATM cell is 53 bytes long. The first 5...

Figure 219 The User Network Interface ATM Cell Header Format

Table 21-2 Fields in an ATM Cell Header Table 21-2 Fields in an ATM Cell Header Controls the flow of traffic across the user network interface and thus into the ATM network. Second 4 bits of Byte 1 and the first 4 bits of Byte 2 Identifies a particular VPC3. A VPC is a group of virtual connections carried between two points and may involve several ATM links. VPIs provide a way to bundle traffic heading to the same destination. Second 4 bits of Byte 2, Byte 3, and the first 4 bits of Byte 4...

Figure 82 IPX Packet Format

The fields of the IPX packet are as follows Checksum A 16-bit field that is set to ones. Packet length A 16-bit field that specifies the length, in bytes, of the complete IPX datagram. IPX packets can be any length up to the media maximum transmission unit (MTU) size. There is no packet fragmentation. Transport control An 8-bit field that indicates the number of routers the packet has passed through. When the value of this field reaches 15, the packet is discarded under the assumption that a...

Figure 83 Ethernet IEEE 8023 and IPX Encapsulation Formats

Ethernet Standard IEEE 802.3 IPX To route packets in an internetwork, IPX uses a dynamic routing protocol called the Routing Information Protocol (RIP). Like XNS, RIP derived from work done at Xerox for the XNS protocol family. In addition to the difference in encapsulation mechanisms, Novell also added a protocol called the Service Advertising Protocol (SAP) to its IPX protocol family. SAP allows nodes that provide services (such as file servers and print servers) to advertise their addresses...

Figure 95 A Sample Apple Talk ZIT

AURP allows a network administrator to connect two or more AppleTalk internetworks through a foreign network (such as Transmission Control Protocol Internet Protocol TCP IP ) to form an AppleTalk wide-area network (WAN). The connection is called a tunnel, which functions as a single, virtual data link between the AppleTalk internetworks, as shown in Figure 9-6.

Figure 96 An Apple Talk Tunnel

A router that connects an AppleTalk internetwork to a tunnel (that is, a router that runs AURP) is called an exterior router. The exterior router sends AppleTalk data packets and routing information through the foreign network by encapsulating the packets with the header information required by the foreign network system. The receiving exterior router removes the foreign header information and sends the packets out the appropriate interface. Packets are encapsulated in User Datagram Protocol...